1. Field of the Invention
The present invention relates to a hybrid vehicle which has a continuously variable transmission using a metal belt, and which is driven by both electric energy and mechanical energy from an internal combustion engine.
This application is based on Japanese Patent Application No. 10-372046, the contents of which are incorporated herein by reference.
2. Description of the Related Art
To reduce emission of toxic substances in the air, electric vehicles have been developed. These electric vehicles, which are driven only by electric energy, have a limited driving range, depending on the capacities of batteries for storing the electric energy. To obtain a sufficient driving range, the batteries must have enormous capacities, which significantly deteriorate the driving performances. Therefore, hybrid vehicles, which use batteries with reduced size, can ensure sufficient driving range, and can improve the driving performances by driving internal combustion engines with fossil fuel while obtaining the mechanical energy and electric energy from the internal combustion engines, have been developed.
Of these hybrid vehicles, a hybrid vehicle which adds a driving/regenerating motor at a predetermined reduction ratio to the driving shaft of a conventional vehicle which has a continuously variable transmission (CVT) using a metal belt, is known. To manufacture this hybrid vehicle, an existing power plant can be utilized as is, and the weight and costs of the system and investment in the manufacturing plant and machinery can be reduced because the additional electrical parts are small.
An example of the hybrid vehicle is shown in FIGS. 4 and 5. FIG. 4 is a schematic diagram showing the power train of the hybrid vehicle 1, and FIG. 5 is a schematic diagram showing the hydraulic circuit of the hybrid vehicle 1.
In the power train shown in FIG. 4, the force from the engine (internal combustion engine) E is input via a torque converter 2 to a forward/reverse switching planetary gear set 3. As shown in FIG. 5, the forward/reverse switching planetary gear set 3 selectively engages with one of frictional elements 6 and 7, which are hydraulically actuated, by a hydraulic switching valve 5 mechanically connected to a select lever 4, in response to the operation of a select lever 4. Thus, the rotational direction of the force from the engine E, which is input to a driving pulley (first pulley) 9 of a CVT 8 shown in FIG. 4, can be switched.
Further, the rotation of the driving pulley 9 is transmitted via a metal belt 10 to a driven pulley (second pulley) 11. The ratio of the rotational speeds of the driving pulley 9 to the driven pulley 11 depends on the wrapping diameters of the metal belt 10 around the pulleys. The wrapping diameters are controlled by pressing forces produced by the oil pressure given to side houses 12 and 13 of the pulleys. The oil pressure is produced by an oil pump (oil pressure producing mechanism) 14 which is driven by the engine E.
The force transmitted to the driven pulley 11 is further transmitted via the final reduction gear (driving force transmitting device) 15 to a drive shaft 16, which drives driving wheels W. The final reduction gear 15 is connected via a gear 17 to the output shaft from the driving/regenerating motor M.
The driving/regenerating motor M is electrically connected to the battery and the motor controller which are not shown.
The hybrid vehicle 1 can convert the kinetic energy of the vehicle into electrical energy (regeneration) by means of the driving/regenerating motor M when the vehicle decelerates. Further, once the engine E is stopped while the vehicle is parked, the vehicle can be restarted by the driving/regenerating motor M in response to the request from the driver. When the driver demands more power, the engine E is additionally started, and the force is transmitted via the CVT 8 to the drive shaft 16, to thereby provide sufficient driving force.
As described above, by adding electrical parts which are smaller than those of an electric vehicle to the metal belt CVT, the kinetic energy of the vehicle can be effectively collected. The engine may be stopped while the vehicle is parked, and therefore the fuel consumption can be remarkably improved.
However, although the above-mentioned hybrid vehicle 1 has improved fuel consumption, the following problems arise.
When driving only by the driving/regenerating motor M while stopping the engine E, the CVT 8 is rotated as the driving/regenerating motor M is rotated, because the output shaft of the driving/regenerating motor M is always connected to the driven pulley 11 of the CVT 8. The force for rotating the CVT 8 becomes a burden on the driving/regenerating motor M, which causes energy loss. Further, in this situation, because the oil pump 14 is driven by the engine E, the oil pressure is not available when the engine E is stopped. Therefore, the pressing forces for rotating the metal belt 10 and the driving and driven pulleys 9 and 11 together without slippage do not act effectively, and the metal belt 10 may slip on the driving pulley 9 and on the driven pulley 11 at a relative speed. The relative slippage between the metal belt and the pulleys must be prevented under all circumstances, and if it is not prevented, their lives may be adversely affected.
Further, when starting the engine E after the starting of the vehicle by the driving/regenerating motor M, the oil pump 11 may be actuated at the same time as the starting of the engine E. When the unstable oil pressure just after the start-up of the oil pump 11 is provided to the frictional elements 6 and 7 and the side houses 12 and 13, the driving force from the engine E may be unstably transmitted to the drive shaft 16.
The present invention is intended to reduce the energy loss caused by driving the vehicle by the motor while stopping the internal combustion engine, and to prevent the degradation of the continuously variable transmission using the metal belt. Further, the present invention is intended to ensure driving comfort when starting the internal combustion engine while driving the vehicle only by the motor.
According to a first embodiment of the present invention, the hybrid vehicle comprises: an internal combustion engine (i.e., an engine E in the embodiment); a continuously variable transmission (a CVT 8 in the embodiment); for transmitting a force between a first pulley (a driving pulley 9 in the embodiment) and a second pulley (a driven pulley 11 in the embodiment) through a metal belt (the metal belt 10 in the embodiment); and a motor (a driving/regenerating motor M in the embodiment), wherein an output shaft of the internal combustion engine is connected to the first pulley, the second pulley is connected to an output shaft of the motor, the output shaft of the motor is connected to a driving force transmitting device (a final reduction gear 15 in the embodiment) for transmitting a driving force from the second pulley and the motor, the motor and the driving force transmitting device are connected to the second pulley via an engaging element (a clutch 22 in the embodiment) for selectively connecting or disconnecting the transmission of the driving force to the second pulley, and the engaging element disconnects the transmission of the force when the internal combustion engine is stopped.
The hybrid vehicle does not transmit the driving force from the motor to the continuously variable transmission when driving the vehicle only by the motor. Thus, the continuously variable transmission does not become a load on the motor.
According to a second invention, the hybrid vehicle of the first invention, the continuously variable transmission presses the metal belt onto the first pulley and onto the second pulley by oil pressure from an oil pressure producing mechanism (an oil pump 14 in the embodiment) which is driven by the internal combustion engine.
Even when driving the vehicle only by the motor while the internal combustion engine is stopped, and when the pressing force between the first and second pulleys and the metal belt is not sufficient because the oil pressure is not provided to the continuously variable transmission, the hybrid vehicle does not rotate the first and second pulleys and the metal belt.
According to a third invention, the hybrid vehicle of the first or second invention, further comprises a transmitted force control mechanism (an electrically controlled pressure control valve 23 in the embodiment) for controlling the transmission of the force through the engaging element when starting the internal combustion engine while driving the vehicle only by the motor.
When starting the internal combustion engine while driving the vehicle only by the motor, the internal combustion engine is not immediately connected to the motor, and this reduces the shock due to the connection. Further, even in the second invention having the continuously variable transmission operated by the oil pressure, the continuously variable transmission is prevented from being rotated when an unstable oil pressure just after the start-up is provided to the continuously variable transmission, and the transmission of the shock to the drive wheels can be avoided.
According to a fourth invention, in the hybrid vehicle of the second or third invention, the engaging element is operated by oil pressure from the oil pressure producing mechanism, connects the transmission of the force when the oil pressure is provided to the engaging element, and disconnects the transmission of the force when the oil pressure is not provided to the engaging element.
The hybrid vehicle simplifies the mechanism for disconnecting the transmission of the force when the internal combustion engine is stopped. Further, by controlling the oil pressure, the transmitted force control mechanism for controlling the transmission of the force is simplified.